Human powered generator

Diagram of the generatorLots of people have built human powered generators. I like this one for two reasons:

1. It's designed to harvest waste energy. (It helps your body stop your knee from swinging at the end of the forward swing, something your body uses energy to do anyways.)

2. The evaluation included serious medical studies to determine the amount of metabolic energy it "takes" from the human.  (to get a watt of power, it increases the human's load by less than a watt. By comparison, a hand crank generator takes 6.4 watts from the human for each watt harvested)

Mythtv gotchas when upgrading from Ubuntu 7.04 (Feisty) to 7.10 (Gutsy)

I upgraded my Mythtv server from Feisty to Gutsy for no good reason (other than I like the pain).

Gotchas I ran into when trying to get MythTV working again:

1. The upgrade lost/removed the libqt3-mysql support from my computer. This resulted in the MythTV applications (frontend and backend) giving "unable to connect to database" errors. As the upgrade had also upgraded my MySQL install, I spent a good amount of time checking that the mythtv user still existed and had the proper permissions before I figured out it was a QT database library problem.
  apt-get install libqt3-mt-mysql fixed it.

2. LIRCD stopped receiving commands from my HDHomeRun receiver from SiliconDust. Turns out you have to change the LIRCD_ARGS="-d 5000" line in the /etc/lirc/hardware.conf file to LIRCD_ARGS="-H udp -d 5000".  After this, typing irw showed that LIRCD was now receiving the command codes as it was supposed to.

3. The module name for my D-Link GWL-G122 usb wifi-adaptor have changed, so I had to change entry in the /etc/modprobe.d/blacklist  file to reflect the new name(s) of: rt2x00usb and rt2500usb.

Riced Dynamo flashlight

On our van trip across the country my aunt and uncle gave us two hand crank (dynamo) LED flashlights which are really useful to keep in the van. The self-charging nature of the flashlights are very nice, in that we can leave them in the van and just wind them up when we need light. Unfortunately, one of the flashlights started to dim and refused to hold a charge. When I got home and opened it up, I found that the rechargeable Li-Ion coin cell inside had died. It originally used a 2032 coin cell rated at 40mAh

Dynamo flashlight opened

Once I had it open, I decided I may as well fix it, and if I was going to be replacing the battery I may as well buy a bigger one (or two) and give the flashlight Continue reading

On the fly external monitor support (mirroring / spanning) on Ubuntu 7.10

My IBM X31 laptop has the capability to drive an external VGA monitor in addition to it's built in XGA (1024×768) Laptop Video Display Screen (LVDS). The new xrandr extension allows non-privlidged users to change monitor layouts on-the-fly. And now, thanks to my friend Tracy, I know the "extra magic" to make it all work.

Continue reading

Failing power supply

Catastrophic failure of a power supply

For my MythTV media computer I use a network based HD-TV tuner from SiliconDust . I've been very pleased with how it works, the form factor and feature set. However, over christmas it suddenly went dead due to no fault of it's own. The 5V 2A power supply had failed. (It is plugged into a UPS with surge suppressor, so I'm relatively sure it was caused by a component failure and not bad input power.) If you look at the photo of the failed power supply (left) next to the replacement component that SiliconDust sent me (right), you can clearly see where something inside melted (and/or forced) the plastic case to bubble out, leading me to believe it was a relatively catastrophic failure.

This reminds me of the trouble I had with the original iRobot Roomba. I had my initial robot replaced under warranty two times  (3 total robots) due to power supply and battery charging issues. Each replacement had a completely new (and different) power supply system, and it was clear that iRobot was iterating through  designs until they found one that was robust.  I only hope that this power supply failure was due to one bad unit, and isn't indicative of the average lifespan of the power supplies supplied with the HDHomerun.

My Reading Habits: Korean

Google Reader (a web based RSS reader that I use to track and read various sites and blogs) has a recommendation system that will give you recommended blogs to subscribe to. It uses the RSS feeds that you are currently subscribed to, and then looks to see who else is also subscribed to those feeds. It then looks for feeds your "neighbors" are subscribed to that you are not subscribed to, and recommends them.

Two of my top three recommendations were in Korean. Juding from the pictures and a few babelfish translations, they are a news website and a fashion/entertainment website.  Two possible conclusions to draw from this:

 1. I'm more like an average korean reader than an average US reader. (Somewhat possible given the  technically orientated blogs I subscribe too.)

2. A lot more Korean uses use Google Reader to read their RSS feeds than English users and are polluting the recommendation system.

My suggestion: Don't recommend a feed that is in a language that the user has never subscribed to before. But wading through a few useless recommendations didn't take much time, and near the bottom of my list was a suggestion for the Girl Genius comic, which I did find useful, so overall I found the recommendation system useful.

Tuning an ext3 filesystem for storing large media files

I added a new hard disk to my MythTV box, specifically for storing movies copied from my DVD collection. Because this disk will be used for storing mostly files that will be in the 1-4GB size range, and because it is NOT going to be used as the root (/) drive of this computer, I set the sparse_super and largefile4 settings, plus reserved zero space for the superuser (-m 0) with the following command:

 
mkfs -t ext3 -m 0 -O sparse_super -T largefile4 /dev/sdb1

MythTV to phone (.3gp) transcoder script and Bluetooth transfer

I built a perl script that can be used as a "User Job" from within mythtv to convert a recorded TV program into a cell phone (.3gp) movie. It makes uses of mythname.pl to get the show and title (for the filename) and mplayer/mencoder and ffmpeg to do the actual transcoding.

Unless you want to drop your files off in the /var/lib/mythtv/for_phone directory, you will need to edit the output directory.  I've found that 35 minutes of TV gets shrunken down to 24-30megs when in .3gp format when transcoded at a generous 80/16 (video/audio bitrate).

Script to transcode from mythtv files to .3gp files

I wrote a second script to transfer any files in this directory to my phone via bluetooth OBEX push every night. I use cron to start the phoneTransfer.pl script up each night, and it looks for any .3gp files in the directory and tries to copy them to my phone. If successful, it removes them from the directory.  Note that my Motorola V3xx has an annoying feature where it will receive OBEX bluetooth files into phone memory, and NOT to the default download location (which can be set to the memory card). If your phone is similar, you will have to copy files from the phone's memory to the memory card so that your phone's memory doesn't get full. If your phone's memory gets full, it will refuse further bluetooth transfers until you move the files over to a memory card. 

Script that does a bluetooth transfer to phone

Note that to use this script you will have to find your phone's bluetooth mac address (using "hcitool scan") and put it in the script. Also, you should pair your phone with your computer, and set your phone up to automatically accept OBEX push/FTP transfers unless you want to manually approve each video transfer.

Cingular/ATT is locking down newer V3XX phones

AT&T Death StarI have one of the first Cingular branded v3xx phones that was released when they first hit the market. Although it came pre-stocked with shortcuts to Cingular stores, Cingular Music downloads, and had things like the IMAP email client disabled by default, it was still relatively easy to hack. I was able to use P2kCommander over a USB cable to enable cool features like allowing unsigned java applications to access the internet , and the IMAP email client.  

To use P2kCommander, you had to go into your Settings->Connection->USB Settings and make sure that the default connection type was set to Data Connection (as opposed to Memory Card or USB Printing). If you couldn't set it to Data Connection, you can't use P2kCommander. (Or use the phone as a modem via a USB cable.)

A reader recently wrote in that Continue reading